Frank e



(N0 Model.)

F. R. OOLV-IN. TELEPHONE TRANSMITTER.

No. 513,305. Patented Jan. 23.. 1894.

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UNITED STATES PATENT @FFICE.

FRAPTK R. OOLVIN, OF NEW YORK, N. Y.

TELEPHONE-TRANSMITTER.

SPECIFICATION forming part of Letters Patent No. 513,305, dated January23, 1894.

Application filed October 10, 1893. Serial No. 487,744. (No model.)

To all whom it may concern:

Be it known that I, FRANK R. OOLVIN, a citizen of the United States,residing in the city, county, and State of New York, have inventedcertain new and useful Improvements in Telephone-Transmitters, of whichthe following is a specification.

This invention relates to telephone transmitters, its object being toproduce a cheap and effective instrument which will not require frequentadjustment and will not deteriorate in transmitting power duringprotracted service.

The invention relates more particularly to transmitters of that type inwhich a body of granular or finely divided conducting material is usedto vary the resistance between circuit electrodes under the impact ofsound waves in the atmosphere, and thus create electrical undulationswhich may be thrown directly into the line, or inductively trans-.

ferred thereto in a way well understood.

The invention comprises a closed receptacle containing the electrodes orterminals of the transmitting circuit, which is filled or partiallyfilled with a granular conducting substance and is sealed to prevent theabsorption of moisture.

It comprises also means for improving the transmitting qualities of theinstrument, by so mounting the diaphragm in relation to the mass ofgranular material that an increased freedom to vibrate will be attained.

Another feature of the invention comprises fixed electrodes incontra-distinction to one or more movable electrodes, whereby changes ofadjustment are rendered unnecessary.

The invention comprises other features of novelty which will be moreparticularly explained hereinafter, and will be definitely in dicated inthe claims appended to this specification.

In the accompanying drawings, which illustrate the invention, Figure 1is a sectional view of a telephone transmitter embodying myimprovements, and Fig. 2 is a perspective view of the closed cellcontaining the electrodes, and which also contains the granularresistance-varying material.

I provide a suitably formed shell A provided with the usual mouth-pieceand recess in the rear, into which recess fits a back piece .ablysemi-cylindrical electrodes E, E, to

which are electrically connected the circuit terminals, as illustrated.The cell D is provided with a sharp edge or rim around its mouth, sothat when it is clamped firmly against the diaphragm, as, for example,by a central bolt F, the diaphragm will be in close contact at allpoints with the sharp edge of the cell. Within the cell is placed a massof conducting or semi conducting granular material, such, for example,as fine granular hard carbon. If the transmitter is to stand verticallythe amount of carbon should be sufficient to contact with bothelectrodes, so that there will be at all times an electric path from oneelectrode to the other. After the diaphragm and cell have beenassembled, they are dipped in or coated with any suitable sealingcompound to exclude air and moisture from the granules.

The lack of uniformity in efficiency of carbon transmitters has beenfound to be largely attributable to the absorption of moisture from theair by the mass of granular carbon, such absorption not only producingan inherent variation of resistance by reason of the presence ofmoisture, but reducing the range of effective resistance by renderingthe edges of the granules softer and smoother. I have found that bysealing the vessel containing the carbon, in the manner described, or inany other suitable way, moisture is offectually excluded andderangements inci dent to its presence are obviated.

- Several other important advantages result from the constructionhereinabove described. The diaphragm being loosely mounted is free tovibrate at its edge and hence there results a greater amplitude ofmovement of its central portions, such movement being less obstructedthan it would be if the diaphragm IOC as well as the circular line ofcontact with the edge of the cell is free; great freedom of movementcombined with elasticity is thus effectually secured. The electrodesbeing fixed with relation to each other the necessity of repeatedadjustment is removed, the varia-' tion of resistance being principallydue to inter-granu1ar change of arrangement of the mass within the cellunder the vibration of the diaphragm, the granules being forced therebytoassume difierent relations'of con tact and thus vary the resistancebetween these fixedelectrod es. The parts may be constructed of anysuitable material. The cylindrical cell is preferably of insulatingmaterial, though it might be of metal covered with insulating material.

As illustrated in the drawings, the electrodes E, E are preferablysemi-cylindrical and are provided with a semi-circular bottom.

There is thus afforded a wide area of contact between the electrodes andthe granular mater'ial,and hence an effective conductive relation isestablished. The electrodes lying in two planes, that is to say, alongthe side wall or wallsof the cell and the bot-tom,it isevident that theintimacy of contact between the mass of granulesand the electrodes willnot be disturbed by a change of position of the transmitter, as gravitywill tend to promote such intimacy whether the bottom of the cell standsin a vertical, horizontal or interme diate plane. Under the impact ofsound waves the diaphragm isthrown into vibration and the granularmaterial contained" in the cell isagitated, varying the resistance'inaccordance withthe degree of agitation.

Having thus described my invention, what I claim as new, and desire tosecure by Letters Patent, is

diaphragm carrying a cell containinga gran- 4 ular conductor and fixedelectrodes relatively non-vibratory in contact with said granularconductor.

3. A telephone transmitter provided with a diaphragm, a cell containinga resistance-Va rying granular material, said cell engaging thediaphragm by a sh'arpedge, and a rigidco'nnection between the cell andthe diaphragm within the area inclosedby said edge.

4. A telephone transmitter provided with a diaphragm carrying an.air-tightcellcontaining granular conducting material in" contact withelectrodes, and fixedel'ect rode's relatively non-vibratory in contactwith said granular material.

5. A telephone trans'tnittercomprising two fixed electrodes, a ca's'efille'd with granular conducting material inclosing the same, said casebeing provided with a sharp edge, and a diaphragmelasticallysupportedagainst' said edge.

6. A telephone transmitter provided with a diaphragm'carryinga cellcontaining granu- 113.1 conducting material, and having fixed electrodesrelatively non-vibratory in the walls of said cell.

7. A telephone transmitter provided with a loosely supported diaphragm,a cellcontaining granular conducting material connected thereto byarigid connection within said cell,

and fixed electrodes in contact withsaid conducting material.

In testimony whereof I have hereunto subscribed my name this 9th day ofOctober, A.

D. 1893. y FRANK R. COLVIN.

Vitnesses:

GEO. M. PHELPS, W. R. HUTCHINS.

